Internal Leakage Control and Venting for ABS Unit

ABSTRACT

A housing block for a hydraulic unit of a vehicle brake system that retaining a piston pump and an eccentric element that rotates the piston. A motor drives the eccentric element within an eccentric chamber. The block has a cylindrical cavity within a hydraulic leakage reservoir and a fluid leakage path that begins near a lower most portion of the eccentric element chamber and extends to a cylindrical cavity by way of a passage defined by an intersection of the eccentric chamber and cylindrical cavity. A pressure equalization path extends from the eccentric chamber upwardly to a point intermediate the housing block and motor enclosure and into the motor enclosure to a location that is substantially above the eccentric chamber. A seal intermediate the motor enclosure and housing block is formed as a closed curve of mastic material encircling the motor shaft, eccentric chamber, hydraulic leakage reservoir hydraulic fluid leakage path, and pressure equalization path.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, in general, to an electronically controlled brake system for automobiles and, more particularly, to an electronically controlled brake system provided with an internal fluid reservoir for receiving leakage brake fluid as well as an internal pressure differential compensating feature.

2. Description of the Related Art

It is desirable to isolate any brake fluid leaking from a braking system pump from the electric motor which powers that pump. This may be facilitated by internal storage of fluid which has leaked as well as avoidance of pressure differentials which might otherwise cause leakage fluid to enter the motor chamber.

A conventional brake system for vehicles consists of a booster and a master cylinder, which form braking fluid pressure in response to a motion of a brake pedal and feeds the fluid pressure to wheel brakes, thus reducing the traveling speed of a vehicle or maintaining a stopped state of the vehicle. However, the vehicles with such conventional brake systems may slip over a road in accordance with road surface conditions or variations in fluid pressure during a braking operation. In an effort to overcome such problems, a variety of electronically controlled brake systems, such as an anti-lock brake system (ABS), a traction control system (TCS) and similar brake control systems have been proposed and widely used. The ABS electronically controls the fluid pressure fed to wheel brakes and prevents slippage of wheels during a braking operation. The TCS is designed to prevent excessive slippage of drive wheels during quick drive or sudden acceleration.

Electronically controlled brake systems frequently employ an electrically powered pump unit including an electric motor, one or more piston pumps, one or more pressure fluid accumulators and other related components. These units are typically sealed against the ingress of external moisture, thus, any fluid which leaks from the piston pumps is not readily removable from the unit. Attempts to form such units as two mutually isolated sub-units (motor and pump) have not proven successful. One problem is that internal heating which occurs during unit operation may create pressure differentials within the unit causing fluid to flow between the sub-units.

A radial piston pump is known, having an electric motor which drives a piston pump arrangement. To keep any leaking hydraulic fluid away from the electric motor, in the housing of the piston pump arrangement collecting chambers and channels are formed, into which leaking hydraulic fluid passes under the action of gravitational and/or centrifugal force in order to be stored there. Disposed between the electric motor and the piston pump arrangement is an open rolling-contact bearing and disposed at the side of the rolling-contact bearing facing the electric motor is a slinger, which is driven by the electric motor. Leaking hydraulic fluid, after it has passed through the open rolling-contact bearing, is kept away from the electric motor by means of the slinger. The radial piston pump may be installed only with a horizontal orientation (with the electric motor next to the piston pump arrangement) or with a vertical orientation such that the electric motor is disposed above the piston pump arrangement, for, if the radial piston pump were to be installed with the electric motor below the piston pump arrangement, the hydraulic fluid under the action of gravitational force alone would flow out of the collecting chambers and the channels into the electric motor, particularly when the electric motor was stopped and the slinger was not driven.

With such pumping sets there is also the problem that because of temperature variations between the interior of the electric motor and the space, in which the eccentric pump arrangement is situated, a (short-term) differential pressure may arise. As a result, excess hydraulic fluid is sucked out of the space, in which the leakage of the eccentric pump arrangement is situated, through the ball bearing or needle bearing for the output shaft and into the interior of the electric motor. Particularly in the event of extended operating times of the pumping set, a significant quantity of hydraulic fluid may escape and be drawn into the electric motor by a vacuum, which arises in the electric motor as a result of short-term cooling in the interior of the electric motor. Conventional scaling methods (sealing rings, sealed bearings etc.) are too expensive and also do not prevent the hydraulic fluid from being dispersed into the environment.

SUMMARY OF THE INVENTION

The present invention provides an internal leakage reservoir in a pump housing designed for sealed ABS hydraulic units where internal hydraulic fluid seepage must be stored inside the unit over the product life

The invention comprises, in one form thereof, a hydraulic pump for a braking system including a pump housing with a cavity for receiving a driving shaft and eccentric and a pair of opposed pump piston cylinders spanning the cavity. There is a pump driving motor having a shaft rotatable about an axis with an eccentric member extending therefrom. The housing and motor have generally planar faces which are sealingly joined along a common surface with the shaft axis extending generally in a horizontal direction orthogonal to the motor and housing surfaces and into the eccentric cavity. A pair of pump pistons are disposed in respective cylinders to be reciprocable therein along a common axis generally orthogonal to the shaft axis in response to eccentric motion. At least one generally cylindrical leakage fluid reservoir is in fluid communication with the eccentric cavity near a lower extremity thereof for receiving leakage hydraulic fluid therefrom and a pressure differential compensating vent is positioned above the eccentric cavity for providing an air path between the housing interior and the motor interior.

Also in general, and in one form of the invention, a hydraulic fluid leakage reservoir or sump is provided in a hydraulic pump housing by creating a blind hole in the housing extending generally orthogonally from a generally planar housing face into the housing and intersecting an eccentric cavity within the housing, and subsequently sealing the open bore end along the housing face byjoining motor and housing faces. A pressure differential vent may be formed in the motor face and, thereafter, the vent sealed from the external environment. Sealing the open bore and sealing the vent may be accomplished simultaneously by applying a viscous sealant or mastic material to one or both of the motor face and housing face, and juxtaposing the housing and motor faces. The eccentric cavity may comprise a blind generally cylindrical bore extending inwardly from the housing face and an undercut region along a portion of the bore cylinder intermediate the ends thereof in which case, the step of creating the blind hole in the housing typically includes intersecting the eccentric cavity only in the undercut region.

An advantage of the present invention is that the location of the reservoir of the present invention prevents hydraulic fluid from entering the electric motor portion of the unit.

Another advantage is the simple arrangement and machining of the cavity with existing tooling. No reservoir cap or other extra parts are necessary.

A further advantage of the present invention is its applicability to a variety of existing hydraulic pump designs by minimal modification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified cross-sectional side view of a sealed hydraulic unit according to the invention in one form;

FIG. 2 is a perspective view of the pump housing of FIG. 1;

FIG. 3 is a cross-sectional view of the pump housing along the lines 3-3 of FIG. 2;

FIG. 4 is a simplified perspective view of the pump housing of FIG. 1;

FIG. 4 a is a simplified perspective view of a reservoir portion of the pump housing of FIG. 4;

FIG. 5 is a side elevation view of a prior art pump housing showing a technique for sealing the junction between the pump housing and motor portion; and

FIG. 6 is a side elevation view of a pump housing similar to FIG. 5, but showing a technique for sealing the junction between the pump housing and motor portion according to the present invention.

Corresponding reference characters indicate corresponding parts throughout the several drawing views.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings and particularly to FIG. 1, there is shown a hydraulic unit 11 which includes a pump housing block 13 and, mounted against the housing block 13, a pump driving motor 15, having motor shaft 27 rotatable about axis 83. The motor is positioned within a motor enclosure or covering hood 17. The pump housing 13 has a generally planar securing face 19 for receiving the motor 15 shown in FIGS. 2, 4 and 6. Extending from this securing face 19 in the housing block 13 is a bore 21 communicating with an undercut region 23, which together define an eccentric chamber. An eccentric member 25 is fixed to the driving shaft 27 which shaft passes through a ball bearing 29 that is supported by the stepped bore 21. The eccentric member alternately actuates a pair of pump pistons (not shown) in cylinders 31 and 33. The eccentric member or element 25 may be a cam element, known swash plate, conventional crank shaft and connecting rod configuration, or other cam-like curves or surfaces may be employed.

In FIG. 3, the pump cylinders 31 and 33 extend along a common axis 85 generally orthogonal to motor shaft axis 81 and are combined with outlet valves generally at 35 and 37 forming two piston pumps that are operative independently of one another. Cylindrical bores 39 and 41 are drilled vertically from below into the housing block 13. In the bores 39 and 41, spring loaded storage pistons (not shown) are located to provide fluid accumulators. Connecting conduits 43 and 45 extend upward from the cylindrical bores 39 and 41 and connect the storage chambers to the inlets of the two piston pumps. Further details of the hydraulic pump unit as thus far described may be gleaned from U.S. Pat. No. 6,142,751.

An internal leakage reservoir is formed by the region 23 in conjunction with a symmetrically disposed pair of blind holes 51 and 53 drilled along axes 59 and 89 parallel to motor shaft axis 83 and orthogonally to the housing block face 19 (FIGS. 2 and 4) which holes intersect the undercut region 23 as best seen in FIG. 4 a. The pump pistons in cylinders 31 and 33 provide pressurized hydraulic fluid to the braking system and some leakage past the pistons into the bore 21 may occur. A hydraulic fluid leakage path extends from the piston cylinders 31 and 33 into bore 21, downwardly into the undercut region 23 and into the bores 51 and 53. This reservoir provides an enlarged interior region into which leakage fluid may drain under the influence of gravity functioning as a sump and allowing storage of hydraulic fluid that seeps from the piston pumps. The fluid is kept away from the electric motor bearing 29 and motor shaft 27, where it could enter the motor and cause premature motor failures. The hydraulic unit of the present invention is designed for deployment with the axis of the motor shaft 27 disposed horizontally with the reservoir cavity located below the piston pump bores 31 and 33 in the pump housing 13, in order to collect and hold the pump seepage by gravity. The reservoir bores 51 and 53 are uniquely arranged to restrict hydraulic fluid from splashing back onto motor shaft 27 during rough road operation of the vehicle. The openings formed where the bores 51 and 53 intersect the undercut region 23 are kept at a maximum to allow the hydraulic fluid to enter the cavity freely. The leakage reservoir must be sufficient in capacity to store the internal leakage over the lifetime of the product.

In FIG. 1, air may surround the motor 15 in region 69 within the motor enclosure 17 as well as occupying the regions 71, 73 and 23 within the pump housing 13. Operation induced temperature variations and the resulting air pressure differentials could cause air to migrate between the pump housing 13 and motor enclosure 17 along the motor shaft 27 and bearing 29. If leakage fluid is present, particularly in cavity 73, that fluid could also move from the pump housing into the motor enclosure. Such leakage fluid migration is minimized by providing an air equalization path identified generally by the arrows 77, 79 and 81 which passes between the housing 13 and enclosure 17 byway of vent 55.

The leakage fluid capacity for one preferred embodiment was approximately 2.6 ml., of which 1 ml. was provided by the undercut region 23. The reservoir cavity was machined in the pump housing as an undercut and two bores, however, depending on the pump housing design, the reservoir could be of a different shape and size. As best seen in FIG. 4 a, the passages or apertures connecting the eccentric cavity and additional seepage reservoirs each had a depth along edge 57 parallel to the bore axis 59 equal to the depth of the undercut. The chord or separation between the edges 57 and 61 was established by the location and diameter of bore 51 with the arcuate length of the opening edges 63 and 65 being somewhat greater. In that preferred embodiment, the motor was vented by a hole 55 in the motor housing face to guarantee equal pressure and free air exchange between the pump housing and motor. This pressure differential vent 55 in the motor face is located above the motor shaft and well above the sump to minimize the likelihood of fluid entering the motor chamber by way of the vent. The technique by which the electric motor is sealed off against the pump housing by the special sealing contour around the cavity to prevent hydraulic fluid from entering along the motor electrical connector 47 is best understood by comparing FIGS. 5 and 6.

In FIG. 5, an illustrative face of a pump housing has an outer bead of sealant, e.g., a silicone or other mastic material, 91 disposed about a closed generally circular path to providing sealing of a pump-motor unit from external dust, moisture and other environmental contaminants. An inner sealant bead 93 provides sealing isolation between the central motor shaft and bearing region 95, and the bore 97 through which electronic control unit power cables such as 47 (FIG. 1) may pass. The sealing technique of FIG. 5 undesirably depends on a motor shaft and bearing seal to prevent leakage fluid ingress into the motor chamber.

FIG. 6, the seal 67 includes an outer sealant bead 99 which provides the same sealing protection as bead 91 in FIG. 5. A second bead of mastic material 101 isolates the electronic control unit power cable opening 103 (along which contamination might enter) from the motor shaft and bearing while leaving the housing facial region 105 unsealed to function as part of the pressure equalization path. An inner seal similar to 93 would block the air pressure equalization path.

The process of providing the hydraulic fluid leakage reservoir in the housing should now be clear. A first blind hole 51 is created in the housing 13 extending generally orthogonally from the housing face into the housing and intersecting the eccentric cavity portion 23 within the housing. The eccentric cavity comprises a blind generally cylindrical bore 21 which extends inwardly from the housing face 19 and the undercut region 23 along a portion of the bore cylinder intermediate the ends thereof and the step of creating the blind hole in the housing includes intersecting the eccentric cavity only in the undercut region. A pressure differential vent 55 is drilled in the motor face, and the vent sealed from the external environment as the open bore end is sealed along the housing face byjoining the motor and housing faces. The steps of sealing the open bore and sealing the vent are performed simultaneously by applying a mastic material to one of the motor face and housing face as illustrated in FIG. 6 before juxtaposing the housing and motor faces. Forming a second cylindrical reservoir portion adds the step of creating an additional blind hole in the housing extending generally orthogonally from the housing face into the housing and intersecting the eccentric cavity within the housing. The open bore end and additional bore end are simultaneously sealed along the housing face by applying a mastic material to one of the motor face and housing face, and joining the motor and housing faces. 

1. In the manufacture of a braking system hydraulic pump having a pump housing with a generally planar face, at least one pump piston reciprocably disposed within the housing, a pump actuating motor having a face joinable to the housing face and having a motor shaft with an eccentric near a free end thereof for drivingly coupling the motor shaft and at least one piston, and an eccentric cavity in the housing for receiving said eccentric, an improved process of providing a hydraulic fluid leakage reservoir in the housing, comprising: creating a blind hole in said housing extending generally orthogonally from said housing face into the housing and intersecting the eccentric cavity within the housing; and sealing the open bore end along the housing face byjoining the motor and housing faces.
 2. The process of claim 1, including the additional steps of forming a pressure differential vent in the motor face, and sealing the vent from the external environment.
 3. The process of claim 2, wherein the steps of sealing the open bore and sealing the vent are performed simultaneously by applying a mastic material to one of the motor face and housing face, and juxtaposing the housing and motor faces.
 4. The process of claim 1, wherein the step of sealing the open bore includes applying a viscous sealant material to one of the motor face and housing face, and juxtaposing the housing and motor faces.
 5. The process of claim 1 wherein the eccentric cavity comprises a blind generally cylindrical bore extending inwardly from the housing face and an undercut region along a portion of the bore cylinder intermediate the ends thereof, the step of boring the blind hole in the housing including intersecting the eccentric cavity only in the undercut region.
 6. The process of claim 1, further including the steps of; creating an additional blind hole in the housing extending generally orthogonally from said housing face into the housing and intersecting the eccentric cavity within the housing; and sealing the open bore end and additional bore end along the housing face by applying a mastic material to one of the motor face and housing face, and joining the motor and housing faces.
 7. A hydraulic pump for a braking system, comprising: a pump housing having a cavity for receiving a driving shaft and eccentric, and a pair of opposed pump piston cylinders spanning the cavity; a pump driving motor and motor enclosure having a shaft rotatable about an axis with an eccentric member extending therefrom, the housing and motor enclosure being sealinglyjoinable along a common generally planar surface with the shaft axis extending generally orthogonal to the planar surface; the pair of pump cylinders adapted to receive respective pistons reciprocable therein along a common axis generally orthogonal to the shaft axis in response to eccentric motion; and a leakage fluid reservoir including a reservoir cylinder in fluid communication with the eccentric cavity for receiving leakage hydraulic fluid therefrom, the reservoir cylinder having an axis extending generally parallel to the shaft axis.
 8. The hydraulic pump of claim 7, wherein the eccentric cavity comprises a blind generally cylindrical bore extending inwardly from the planar surface, and an undercut region along a portion of the bore cylinder intermediate the ends thereof, the leakage fluid reservoir cylinder being in fluid communication with the eccentric cavity solely in the undercut region.
 9. The hydraulic pump of claim 7, wherein the housing and motor enclosure are sealingly joined along the common surface, and further including a pressure differential compensating vent providing an air path between the housing interior and the motor interior.
 10. The hydraulic pump of claim 7, wherein the leakage fluid reservoir includes a lowermost portion of the eccentric cavity and a second reservoir cylinder in fluid communication with the eccentric cavity for receiving leakage hydraulic fluid therefrom, the second reservoir cylinder having an axis extending generally parallel to the shaft axis.
 11. A hydraulic pump for a braking system, comprising: a pump housing having a cavity for receiving a driving shaft and eccentric, and a pair of opposed pump piston cylinders spanning the cavity; a pump driving motor and motor enclosure having a shaft rotatable about an axis with an eccentric member extending therefrom, the housing and motor enclosure being sealingly joinable along a common surface with the shaft axis extending generally in a horizontal direction into the eccentric cavity; the pair of pump cylinders adapted to receive respective pistons reciprocable therein along a common axis generally orthogonal to the shaft axis in response to eccentric motion; a leakage fluid reservoir including a reservoir cylinder in fluid communication with the eccentric cavity for receiving leakage hydraulic fluid therefrom; and a pressure differential compensating vent positioned above the eccentric cavity for providing an air path between the housing interior and the motor enclosure interior.
 12. The hydraulic pump of claim 11, wherein the reservoir cylinder has an axis extending generally parallel to the shaft axis.
 13. The hydraulic pump of claim 11, wherein the eccentric cavity comprises a blind generally cylindrical bore extending inwardly from the common surface, and an undercut region along a portion of the bore cylinder intermediate the ends thereof, the leakage fluid reservoir cylinder being in fluid communication with the eccentric cavity solely in the undercut region.
 14. The hydraulic pump of claim 13, wherein the undercut region comprises a portion of a cylinder of diameter and axial extents both less than the respective diameter and axial extents of the bore cylinder.
 15. The hydraulic pump of claim 13, wherein the leakage fluid reservoir includes the undercut region of the eccentric cavity and a second reservoir cylinder in fluid communication with the eccentric cavity undercut region for receiving leakage hydraulic fluid therefrom, the second reservoir cylinder having an axis extending generally parallel to the shaft axis.
 16. A hydraulic unit of a vehicle brake system, comprising a housing block, at least one piston pump retained inside the housing block having a piston with an eccentric element that displaces the piston, an eccentric element chamber within the housing block in which said eccentric element is rotatable, a motor for driving said eccentric element, a motor enclosure, a hydraulic leakage reservoir comprising at least one generally cylindrical cavity in said housing block, a hydraulic fluid leakage path that begins near a lower most portion of the eccentric element chamber and extends to the at least one generally cylindrical cavity through a passage comprising an intersection of the eccentric element chamber and cylindrical cavity, and a pressure equalization path extending from the eccentric element chamber upwardly intermediate the housing block and motor enclosure and into the motor enclosure at a location substantially above the eccentric chamber.
 17. A hydraulic unit in accordance with claim 16, further comprising a seal intermediate the motor enclosure and housing block formed as a closed curve of mastic material encircling the motor shaft, eccentric chamber, hydraulic leakage reservoir, hydraulic fluid leakage path, and pressure equalization path. 